Digital recording and reproduction apparatus for videos and audios using disk media have become widespread. In these apparatus, there is a demand for development of technologies which realize the audio-dubbing function at a low cost similar to tape media. The audio-dubbing function is a function which allows information, especially audios to be additionally recorded over already recorded audios and videos.
Mentioned as a prior art example of realizing the audio-dubbing function with disk media is Japanese Patent Application Laid-Open Hei 5 No.234084. This technology, by taking advantage of the fact that the reading time of data is shorter than the program presentation time, writes input audio-dubbing data on the disk in the duration after the data to be currently presented has been loaded from the disk into the memory and until the time the next data will be loaded. That is, this method is able to realize audio dubbing using a single disk recording and reproduction device.
Here, the term program presentation time indicates the playback time unique to each program such as video, music etc. For example, a one-minute video must be played back as exactly one minute even if it is played back with a different playback device.
FIG. 22 shows a recording format on a disk in the prior art. This disk is formatted with a series of ECC (error correction cording) blocks. This ECC block is the minimum unit for encoding in which data is added with error correction parities and encoded. For reading data, each block of data is read out as a unit and error corrected to extract the necessary data. On the other hand, data rewriting is performed by reading each ECC block of data, performing error correction, renewing the necessary part of the error corrected data, re-assigning error codes to the data and recording it on the disk. This means that even when only one byte of data needs to be rewritten, the entire ECC block which includes that byte of data should be read out and renewed.
In each ECC block, video data and audio data are arranged as shown in FIG. 22(b) sequentially in the order of an audio dubbing block, original audio block and original video block. In each block, the dubbed audio, original audio and original video corresponding to approximately the same period of time are included. Herein, the original audio block together with the original video block will be called an original block. When an original program (a video data prior to recording of a dubbing audio data) needs to be recorded, dummy data should be written beforehand into audio dubbing blocks.
Next, the operation of audio dubbing in the prior art will be described with reference to FIG. 23. In this figure, the chart at the top shows associated means and the relationship between the associated means and processed positions on the recording medium. The chart at the middle shows the position of the head in the disk and the chart at the bottom schematically shows the ratio of the program data occupied in a buffer memory 108.
Here, a program is allotted to a continuous area s11-s18 on the disk, where areas s11-s13, s13-s15 and s15-s17 represent individual ECC blocks and areas s11-s12, s13-s14, s15-s16 and s17-s18 correspond to individual audio dubbing blocks (s11 and s12 represent points on the disk).
At time t1, the data from the area up to s13 has been stored in buffer memory 108, and the data recorded in area s11-s13 is decoded and presented (played back) whilst dubbed voice corresponding to that data is being input and encoded.
During the period of time t1 to t3, the data in area s13-s15 is loaded from the disk into buffer 108 and an audio dubbing buffer. The audio dubbing buffer holds the read ECC block as is, which has the same structure as shown in FIG. 22(b).
At time t2, decoding and playing back of the data recorded in the area s11-s1, which was being done at time t1, ends. After time t2, the data read out from the area s13-s15 during the period from time t1 to t3 is decoded and played back whilst voice dubbing corresponding to that data is being input and encoded. Decoding and playing back of the data belonging to this area s13-s15 continues until time t5.
Encoding of the voice dubbing having been input up to time t2 is completed at least before time t3. At time t3, the voice dubbing having been input up to time t2 starts to be recorded to the disk medium. Though some time is needed to wait the disk to turn for accessing s11, this time is short compared to the time for data to be read from or written to the disk so no consideration is given herein.
Writing dubbed sound to the disk is performed from time t3 to t4. When this writing to the disk completes at time t4, the data belonging to the area s15-s17 on the disk starts to be loaded from time t4. In this way, the same processing sequence is repeated from this point and thereafter.
In this prior art, use of the advantage that the reading time of data is shorter than the playback time of the data as a result of data compression is made so as to enable a single recording and reproducing means to realize audio dubbing by controlling the recording and reproducing means time-divisionally for both recording and reproduction.
As has been described, since error correction coding is performed for each ECC block as a unit, even if only one byte of data in an ECC block needs to be renewed, it is necessary to read and rewrite the entire ECC block involving that byte of data. When pieces of audio dubbing data are diversely distributed in ECC blocks as in the above prior art, it is necessary to rewrite almost all ECC blocks or all data in order to record audio dubbing data. In order to perform audio dubbing by rewriting many ECC blocks, a disk drive having high-speed reading/writing performance should be used or the amount of data to be read and written should be reduced.
Use of a disk drive having high-speed reading writing performance is expensive compared to that of low speed. Further, a higher power consumption is needed because of enhancement of the rotating speed of the disk. On the other hand, if it is attempted to realize audio dubbing with a disk drive of a low speed, the image quality should be compromised to reduce the amount of data.
The present invention has been devised in view of the above problems of the prior art, it is therefore an object of the present invention to realize audio dubbing, using a disk drive of a relatively low data transfer rate in a configuration where recording and reproduction can be performed only by ECC block units and still without either causing any time lag with respect to the original video or compromising any image quality.